In an internal combustion engines such as a Diesel engine and a gasoline engine, even if combustion is stopped in a combustion chamber, a piston performs reciprocal motion tens of times until inertia of the piston is consumed by friction, thereby vibrating an engine. Conventionally, in order to reduce the vibration, a throttle valve on an intake air passage is completely closed when the engine is being stopped. However, when the throttle valve is completely closed to close the intake air passage, a large negative pressure is generated in the intake air passage because the piston continues reciprocal motion for a while after combustion is stopped. In this condition, because the air amount in the cylinder is reduced in a compression stroke, the piston receives reduced resistance against inertia energy of the reciprocal motion of the piston. Therefore, the piston moved by inertia tends to stop near the top dead center.
Japanese Patent Publication Laid-Open No. 2000-213375 (Patent Document 1) describes that, when the piston stopped near the top dead center, a crank arm and a crank rod are arranged in tandem, and a large torque is required to move the piston, and therefore startability of the engine is degraded. Therefore, Patent Document 1 proposes that the throttle valve is slightly opened to weaken the negative pressure in the intake air passage when an engine revolving speed is lower than a predetermined value due to the inertia during stopping of the engine.
Japanese Patent Publication Laid-Open No. 06-307264 (Patent Document 2) describes about stopping ignition signals when the engine revolving speed becomes a predetermined value or less in stopping the engine.
Japanese Patent No. 4066642 (Patent Document 3) describes that, in stopping an engine, after fuel injection is stopped, ignition control is continued until a fuel cycle elapses at least two times in each cylinder. Thus, production of un-combusted fuel is prevented, which otherwise flows into an exhaust system.
Japanese Patent Publication Laid-Open No. 2007-63997 (Patent Document 4) describes that ignition timing is retarded responsive to change in pressure in the intake pipe during deceleration of a vehicle to prevent the engine revolving speed from blowing up. Japanese Patent No. 3321021 (Patent Document 5) and Japanese Patent Publication Laid-Open No. 2003-176772 (Patent Document 6) disclose feedback control for advancing and retarding the ignition timing.